1. Field of the Invention
The present invention relates to a liquid crystal display device with a touch screen, and particularly to a liquid crystal display device with a touch screen having capacitive high-transmittance touch screen function.
2. Background Art
An IPS liquid crystal display device is known as one type of liquid crystal display devices. In an IPS liquid crystal display device, pixel electrodes and counter electrodes are formed on the same substrate and an electric field is applied between each pair of the pixel electrodes and the counter electrodes to rotate liquid crystal molecules in the substrate plane for contrast control. The IPS liquid crystal display device is therefore characterized in that the grayscale of a displayed image is not reversed when the screen is viewed in an oblique direction.
The IPS liquid crystal display panel has no counter electrode on the substrate on which color filters are provided, unlike a TN liquid crystal display panel and a VA liquid crystal display panel. Therefore, to reduce display noise and from other reasons, a transparent conductive layer is formed on the front side of the color filter substrate (the side opposite to where the color filters are provided) (see Japanese Patent No. 2,758,864).
In recent years, widespread use of mobile devices increases the importance of the touch screen technology that supports a “user friendly” graphical user interface.
A capacitive touch screen is known as one of the touch screen technologies. A typical capacitive touch screen includes a touch screen substrate in which a conductive coating (transparent conductive layer) is applied on the front side (and the backside) of a glass substrate, and position detection is carried out when a finger of an operator touches the touch screen substrate.
A liquid crystal display device having the above touch screen substrate attached to the front side of the liquid crystal display panel is also known as a liquid crystal display device with a touch screen. In such a liquid crystal display device with a touch screen, when a finger of the operator touches the menu screen displayed on the liquid crystal display panel, the display device is operated according to the selected menu (see “Development of capacitive high-transmittance touch screen”, Saburo Miyamoto and four others, SHARP Technical Report, 92, August, 2005, pp. 59-63) (hereinafter referred to as Document 1).
Related art documents relevant to the invention include Japanese Patent No. 2,758,864 and “Development of capacitive high-transmittance touch screen”, Saburo Miyamoto and four others, SHARP Technical Report, 92, August, 2005, pp. 59-63.